The background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
The performance requirements of a WiGig baseband signal-processing system are three-fold. Based on input signal levels, it is desirable to generate sufficient gain for maximum signal-to-noise (SNR) ratio at the baseband output. It is also desirable to attenuate out-of-band signals with respect to a specified rejection level and be able to accommodate input signals that have a high dynamic range while maintaining high linearity.
FIG. 1 is a diagram of a baseband system in which a filter function is realized with a first dedicated amplifier in a closed-loop configuration coupled to a second dedicated amplifier configured to provide programmable gain. The first stage is a Sallen-Key filter, which has a large input impedance and a small output impedance. The input to the filter is via resistor R1, whose output is coupled to resistor R2 and capacitor C3, which couples to the output Vout. Resistor R2 is coupled to capacitor C4 (which is grounded) and the positive input of the operational amplifier. The output Vout is directly coupled to the negative input of the operational amplifier to function as a unity-gain buffer. The operational amplifier offers high gain and allows the construction of a second-order filter without the use of inductors. In this case, the impedances depicted in this Sallen-Key filter provide a low pass filter. These filters can be designed as low-pass, high-pass, or band-pass filters. The second stage provides adjustable gain via the adjustable impedances Radj(1) and Radj(2) depicted in FIG. 1.